Ferripolyphosphates



United States Patent 3,403,971 FERRIPOLYPHOSPHATES James F. Hazel andWallace M. McNabb, Havertown, and Mary Kieran McElroy, Philadelphia,Pa., assignors, by mesne assignments, to Research Corporation, New York,N.Y., a nonprofit corporation of New York No Drawing.Continuation-impart of application Ser. No. 472,665, July 16, 1965. Thisapplication Feb. 20, 1967, Ser. No. 617,045

21 Claims. (Cl. 23-105) ABSTRACT OF THE DISCLOSURE Novelferripolyphosphates have molar Fe O /P O ratios from 0.35 to 0.5corresponding to the empirical formula Fe (OH) (PO) -nH O wherein x hasany value from 0.5 to 2, y is 6-x and n is any value from 0 to 15. Theymay be made by admixing a water-soluble ferric salt and an alkali metalglassy polyphosphate or the free acid thereof in the presence of waterin the proportion of about one mole of iron to three moles of P0 groups.They are good reversible adsorbents of water and they adsorb ammonia andother Lewis bases.

This application is a continuation-in-part of application Ser. No.472,665, now abandoned, filed July 16, 196-5.

The invention relates to novel ferripolyphosphates having molar Fe O /PO ratios from 0.35 to 0.5 corresponding to the empirical formula Fe(OI-I) (PO -nl-I O wherein x has any value from 0.5 to 2, y is -6x and nis any value from 0 to 15. They are good reversible adsorbents of waterand they adsorb ammonia and other Lewis bases.

The ferripolyphosphates of the invention may be made by adding anaqueous solution of an alkali metal glassy polyphosphate to an aqueoussolution of a water-soluble ferric salt. A yellow fiocculent precipitateis first formed which changes to a granular white solid as furtherglassy polyphosphate is added up to about 3 moles of (P0 groups per moleof iron. The addition of further polyphosphate causes the precipitate todissolve but the ferripolyphosphate of the invention can be preparedfrom such solutions by precipitating the alkali metal iron phosphatecomplex with a water-miscible organic liquid such as methanol, ethanol,dioxane, acetone, 2-propanol or l-propanol, disolving the precipitate inwater, and then adding this solution (I) to a ferric salt solution untilthe molar FO /Fe ratio is about 3. Alternatively, the solution referredto above as I may be passed through a cation exchange resin in thehydrogen form to convert the complex to the free acid and adding thissolution to a ferric salt solution. The solution of the soluble alkalimetal iron phosphate complex may also be formed by rapidly mixing aferric salt solution with a solution of glassy alkali metalpolyphosphate in the ratio of one mole of iron to six moles of P0groups. The solution of the complex then is mixed rapidly with an amountof ferric salt solution sufficient to bring the molar PO /Fe ratio toabout 3. In this procedure the fiocculent yellow precipitate does notappear but a white ferripolyphosphate gel is directly produced.

Phosphate chain\ 0\(|)/O\|O/O\ (l)/0\ i i Phosphate chain 0 0 03,403,971 Patented Oct. 1, 1968 The ferripolyphosphate also may beprepared by passing a solution of alkali metal glassy polyphosphatethrough a cation exchange resin in the hydrogen form in order totransform the phosphate to the free acid, followed by the addition ofthis solution to a solution of ferric salt in water or a water-miscibleorganic liquid such as methanol. The precipitate which forms isseparated by filtration and washed with the organic liquid.

In general, the products obtained by adding alkali metal glassypolyphosphate solutions which are about 3 M as to P0 groups to 0.5 molarferric salt solutions until the ratio of P0 groups to iron atoms is alittle less than 3 to 1, are of superior uniformity and adsorptivecapacity.

The following are illustrative examples of methods of preparing theferripolyphosphate compositions of the invention:

EXAMPLE 1 An aqueous solution of glassy sodium polyphosphate is preparedby dissolving 30.5 g. of glassy sodium polyphosphate (Calgon R-SUnadjusted Form of Calgon Company) in rapidly stirred water to give atotal volume of ml. This 3 molar P0 solution is added with stirring to a0.5 M aqueous solution of ferric chloride until the flocculent yellowprecipitate which first forms is changed to a white precipitate. Thetotal addition of phosphate is kept at slightly less than 3 moles of P0groups per mole of iron. Care is taken to avoid an excess ofpolyphosphate to prevent dissolution of the precipitate, by testing forcomplete precipitation of the iron with KCNS. The precipitate isfiltered off and redispersed in water only once (because of the tendencyof the precipitate to peptize in water). Further redispersion in thewater-miscible organic liquid and filtration are continued until thewashings are substantially free of sodium and chloride. The precipitatemay be air dried on porous plates or paper pads and may be further driedby evacuation or by heating in an oven at about 108 C. for one or twohours.

EXAMPLE 2 A 3 molar P0 solution is prepared as described in Example 1.This solution is mixed rapidly with a 0.5 M aqueous solution of ferricchloride in the ratio of slightly less than 3 moles of P0 groups permole of iron to form a white gel. The gel is allowed to shrink andextrude liquid (undergo syneresis) for a few hours. The liquid isdiscarded. The gel is leached with water, followed by leaching with awater-miscible organic liquid, in order to decrease the sodium chloridecontent of the gel. The gel is then dispersed in the organic liquid,filtered and dried as in Example 1.

The ferripolyphosphate product made in this manner has a molar Fe O /P Oratio of about 0.4. Neglecting the presence of residual products ofmetathesis such as sodium chloride, as well as varying amounts of otherphosphates formed by hydrolysis of P0 groups, the product may berepresented by the empirical formula Fe11P2qO 4'xH20, or (PO3)5'HH2O asWell as the structural formula:

0 O O O\? O\()/O\(l)/O\?/O\ Phosphate chain L/ L/ I Fe (B (5 0 0 0 OPhosphate chain ..9 5 H20"? H20 H20 H20 H O H2O Relative humidity,percent: Adsorption, mg./ gm.

Desorption at 0.1 atmosphere ressure for one-half hour at roomtemperature amounts to about 40% of the initial adsorption and showsgood cyclin performance.

The specific surface area of this sample calculated on the assumption ofa monomolecular layer of adsorbed water is 660 square meters per gram.Even higher specific surface area, up to about 1200 square meters pergram can be obtained with milder drying conditions.

Similar gels may be made by sprinkling solid powdered glassy sodiumpolyphosphate on the surface of 0.5 M aqueous ferric chloride solutionwith stirring in the ratio of slightly less than 3 moles of P groups toone mole of iron.

Gels having similar properties may be made by admixing comminuted ferricsalt such as FeC1 -6H O with powdered glassy sodium polyphosphate in theratio of at least one mole of iron to three moles of P0 groups, andslowly stirring the mixture into water in sufficient volume to permitthe reaction to go to completion as judged by the precipitate becomingwhite on standing.

Ferripolyphosphate gels made by gradually adding aqueous solutions ofglassy sodium polyphosphate that are less concentrated than about 3molar in P0 groups to aqueous ferric chloride solutions lessconcentrated than about 0.5 M tend to be more basic in composition.Thus, the gradual addition of a glassy sodium polyphosphate solutionthat has a concentration of 0.6 molar in P0 groups to a 0.1 M aqueoussolution of ferric chloride yields a ferripolyphosphate gel having amolar Fe O /P O ratio of about 0.48, and an empirical formula: Fe (OH)(PO -nH O.

The ferripolyphosphate gels made by any of the methods described hereinmay be stored in the wet state in airtight containers for eventual usewithout subjecting them to a drying operation or they may be convertedinto aquasols by washing the gels with water until a major portion ofthe gel forms a stable aqueous dispersion.

We claim:

1. A ferripolyphosphate having a molar Fe O /P O ratio between 0.35 and0.5 and the empirical formula Fe (OH) (PO 'nH O wherein x is any valuefrom 0.5 to 2, y is 6-x and n is any value from 0 to about 15.

2. A ferripolyphosphate as defined in claim 1 wherein n is a valuebetween about 4 and about 8.

3. A ferripolyphosphate as defined in claim 1 wherein the molar Fe O /PO ratio is about 0.4.

4. A ferripolyphosphate a-s defined in claim 3 wherein n is a valuebetween about 4 and about 8.

5. A method of making ferripolyphosphate which comprises admixing awater-soluble ferric salt and an alkali metal glassy polyphosphate orthe free acid thereof in the presence of water in the proportion ofabout one mole of iron to three moles of P0 groups.

6. A method of making a ferripolyphosphate which comprises adding anaqueous solution of an alkali metal glassy polyphosphate to an aqueoussolution of a watersoluble ferric salt until the iron is substantiallycompletely precipitated, separating the precipitate and drying theseparated precipitate to a water content between 0 and about weightpercent.

7. The method of claim 6 wherein the separated precipitate is washedwith a water-miscible organic liquid.

8. The method of claim 7 wherein the separated precipitate is dried to awater content between about 12 and about 22 weight percent.

9. A method of making a ferripolypohsphate which comprises adding anaqueous solution of about 300 grams of glassy sodium polyphosphate perliter to about a 0.5 molar aqueous solution of a water-soluble ferricsalt until the iron is substantially completely precipitated, washingthe precipitate at least once with water and then with a water-miscibleorganic liquid and separating the precipitate.

10. The method of claim 9 wherein the separated precipitate is drieduntil said precipitate contains between 0 and about 35 weight percent ofwater.

11. The method of claim 9 wherein the separated precipitate is dried toa water content between about 12 and about 22 weight percent.

12. A method of making a ferripolyphosphate which comprises adding anaqueous solution of a glassy alkali metal polyphosphate to an aqueoussolution of a watersoluble ferric salt until the precipitate initiallyformed redissolves, adding a water-miscible organic liquid untilprecipitation ceases, separating the precipitate dissolving it in water,adding this solution to a ferric salt solution, separating theprecipitate, and drying the separated pre cipitate to a water contentbetween 0 and about 35 weight percent.

13. A method of making a ferripolyphosphate which comprises adding anaqueous solution of a glassy alkali metal polyphosphate to an aqueoussolution of a watersoluble ferric salt until the precipitate initiallyformed redissolves, adding an aqueous 0.5 M solution of a ferric saltuntil precipitation is complete, washing the precipitate with water andthen with a water-miscible organic liquid, separating the precipitate,and drying the separated precipitate to a water content between 0 andabout 35 weight percent.

14. The method of claim 12 wherein the alkali metal polyphosphate isglassy sodium polyphosphate.

15. The method of claim 13 wherein the alkali metal polyphosphate isglassy sodium polyphosphate.

16. The method of claim 15 wherein the glassy sodium polyphosphate hasan average of about 9 phosphorus atoms per chain.

17. The method of claim 12 wherein the separated precipitate is dried toa water content between about 12 and about 22 weight percent.

18. A method of making a ferripolyphosphate which comprises passin anaqueous solution of a glassy alkali metal polyphosphate through a cationresin in the hydrogen form to convert the phosphate to the free acid,adding this solution to a water solution of a water soluble ferric saltuntil the ratio of P0 groups to iron atoms is about 3 to 1, separatingthe precipitate, and drying the precipitate to a water content between 0and about 35 weight percent.

19. The method of claim 18 wherein the separated precipitate is dried toa water content between about 12 and about 22 weight percent.

20. A method of making a ferripolyphosphate which comprises slowlyadding solid powdered glassy sodium polyphosphate to an aqueous solutionof 0.5 molar ferric chloride until the ratio of P0 groups to iron atom-sis about 3 to 1, separating the precipitate, and drying the precipitateto a water content of between 0 and about 35 weight percent.

21. A method of making a ferripolyphosphate aqueous dispersioncomprising adding an aqueous solution of an alkali metal glassypolyphosphate to an aqueous solution of water-soluble ferric salt untilthe iron is substantially completely precipitated and washing theprecipitate with 5 6 water until a major portion of the precipitateforms a Phosphates, Soil Science, vol. 88, No. 3, September stableaqueous dispersion. 1959, pp. 130-132.

Gmelins: Handbuch der Anorganischen Chemie, 8 Referemes clted Auflage,TEIL. B LIEF. 1-5 System No. 59, 1932 pp. UNITED STATES PATENTS 5 768and 770. U I 2,414,974 1/1947 Nielson 23 105 33 'g gfig fgfl f g ChumMmerale 3,014,784 12/1961 Knight et a1. 23-105 OTHER REFERENCES OSCAR R.VERTIZ, Primary Examiner.

W. E. Cate et al.: Preparation of Crystalline Ferric 10 L. A. MARSH,Assistant Examiner.

